/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.result.condition;

import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Set;

import org.springframework.lang.Nullable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.cors.reactive.CorsUtils;
import org.springframework.web.server.ServerWebExchange;

/**
 * A logical conjunction (' && ') request condition that matches a request against
 * a set of header expressions with syntax defined in {@link RequestMapping#headers()}.
 *
 * <p>Expressions passed to the constructor with header names 'Accept' or
 * 'Content-Type' are ignored. See {@link ConsumesRequestCondition} and
 * {@link ProducesRequestCondition} for those.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public final class HeadersRequestCondition extends AbstractRequestCondition<HeadersRequestCondition> {

    private static final HeadersRequestCondition PRE_FLIGHT_MATCH = new HeadersRequestCondition();


    private final Set<HeaderExpression> expressions;


    /**
     * Create a new instance from the given header expressions. Expressions with
     * header names 'Accept' or 'Content-Type' are ignored. See {@link ConsumesRequestCondition}
     * and {@link ProducesRequestCondition} for those.
     *
     * @param headers media type expressions with syntax defined in {@link RequestMapping#headers()};
     *                if 0, the condition will match to every request
     */
    public HeadersRequestCondition(String... headers) {
        this(parseExpressions(headers));
    }

    private HeadersRequestCondition(Collection<HeaderExpression> conditions) {
        this.expressions = Collections.unmodifiableSet(new LinkedHashSet<>(conditions));
    }


    private static Collection<HeaderExpression> parseExpressions(String... headers) {
        Set<HeaderExpression> expressions = new LinkedHashSet<>();
        if (headers != null) {
            for (String header : headers) {
                HeaderExpression expr = new HeaderExpression(header);
                if ("Accept".equalsIgnoreCase(expr.name) || "Content-Type".equalsIgnoreCase(expr.name)) {
                    continue;
                }
                expressions.add(expr);
            }
        }
        return expressions;
    }

    /**
     * Return the contained request header expressions.
     */
    public Set<NameValueExpression<String>> getExpressions() {
        return new LinkedHashSet<>(this.expressions);
    }

    @Override
    protected Collection<HeaderExpression> getContent() {
        return this.expressions;
    }

    @Override
    protected String getToStringInfix() {
        return " && ";
    }

    /**
     * Returns a new instance with the union of the header expressions
     * from "this" and the "other" instance.
     */
    @Override
    public HeadersRequestCondition combine(HeadersRequestCondition other) {
        Set<HeaderExpression> set = new LinkedHashSet<>(this.expressions);
        set.addAll(other.expressions);
        return new HeadersRequestCondition(set);
    }

    /**
     * Returns "this" instance if the request matches all expressions;
     * or {@code null} otherwise.
     */
    @Override
    @Nullable
    public HeadersRequestCondition getMatchingCondition(ServerWebExchange exchange) {
        if (CorsUtils.isPreFlightRequest(exchange.getRequest())) {
            return PRE_FLIGHT_MATCH;
        }
        for (HeaderExpression expression : this.expressions) {
            if (!expression.match(exchange)) {
                return null;
            }
        }
        return this;
    }

    /**
     * Compare to another condition based on header expressions. A condition
     * is considered to be a more specific match, if it has:
     * <ol>
     * <li>A greater number of expressions.
     * <li>A greater number of non-negated expressions with a concrete value.
     * </ol>
     * <p>It is assumed that both instances have been obtained via
     * {@link #getMatchingCondition(ServerWebExchange)} and each instance
     * contains the matching header expression only or is otherwise empty.
     */
    @Override
    public int compareTo(HeadersRequestCondition other, ServerWebExchange exchange) {
        int result = other.expressions.size() - this.expressions.size();
        if (result != 0) {
            return result;
        }
        return (int) (getValueMatchCount(other.expressions) - getValueMatchCount(this.expressions));
    }

    private long getValueMatchCount(Set<HeaderExpression> expressions) {
        long count = 0;
        for (HeaderExpression e : expressions) {
            if (e.getValue() != null && !e.isNegated()) {
                count++;
            }
        }
        return count;
    }


    /**
     * Parses and matches a single header expression to a request.
     */
    static class HeaderExpression extends AbstractNameValueExpression<String> {

        public HeaderExpression(String expression) {
            super(expression);
        }

        @Override
        protected boolean isCaseSensitiveName() {
            return false;
        }

        @Override
        protected String parseValue(String valueExpression) {
            return valueExpression;
        }

        @Override
        protected boolean matchName(ServerWebExchange exchange) {
            return (exchange.getRequest().getHeaders().get(this.name) != null);
        }

        @Override
        protected boolean matchValue(ServerWebExchange exchange) {
            return (this.value != null && this.value.equals(exchange.getRequest().getHeaders().getFirst(this.name)));
        }
    }

}
